Apparatuses for quality control of mechanical pieces such as bolts and screws and similar are commonly used to select mechanical pieces which do not come within a specific dimensional tolerance.
In particular, some mechanical pieces such as special bushes, molded or machined nuts or inserts, bar or wire pieces machined on a double lathe, pieces obtained through hot or cold molding based on drawings, punching or machining, must meet a very high quality standard, meeting strict dimensional tolerances.
For example, for a mechanical piece with a diameter of 3 mm and a length of 8 mm, a dimensional tolerance of ±0.01 mm can be required.
In order to detect such tolerances, the control apparatus must be provided with operation stations for controlling the mechanical pieces, comprising artificial vision systems, laser sensors, gauges, feeler pins and so on and with a conveyor belt which positions the mechanical piece near each operation station.
The movement of the conveyor belt is programmed so that the mechanical piece transits at an operation station long enough to allow the station to control said piece.
If the mechanical piece transits in front of all the operation stations and no tolerance defect is detected, the mechanical piece is selected, otherwise it is rejected.
Other control apparatuses are known with a rotating table.
Said control apparatuses comprise an operation station where the mechanical pieces are loaded, for example fed by a piece-holder placed outside the automatic machine, a rotating table where the pieces are deposited by means of the loading operation station and a plurality of control operation stations fixed around the rotating table.
In some control apparatuses, the number and type of control operation stations can be varied, by mounting or removing control operation stations around the rotating table, according to the space available and the size of the single stations.
The table can be rotated at a predetermined angular pitch, i.e. alternating predetermined angular pitch rotations with predetermined time intervals when the rotating table is substantially fixed with respect to the stations.
In order to control the pieces, the loading operation station deposits the mechanical pieces, one at a time, on the rotating table so that the piece transits at the control operation stations; the rotating table is programmed so that the piece stops at each station for a predetermined length of time; sufficient to control the dimensional tolerances.
Several mechanical pieces, loaded one at a time by the loading operation station, can be present at the same time on the rotating table and can be controlled at the same time by the control operation stations.
In this way, the time required by a first control operation station to finish a first control of a first mechanical piece is exploited by a second control operation station to carry out a second control of a second mechanical piece.
Each mechanical piece is either selected or rejected substantially at the end of a rotation of the rotating table, i.e. after stopping for the predetermined time at the control operation stations.
Even if the above-mentioned control apparatuses make it possible to identify defects within very severe dimensional tolerances, they have some evident limitations.
The need to control a high number of mechanical pieces in a short time and the need to guarantee strict tolerance for each piece makes it imperative to optimize the efficiency of the control apparatus, i.e. to increase the number of mechanical pieces which can be controlled in the time unit.
However, with the control apparatuses currently available it is not possible to increase the number of pieces controlled per time unit, since each single control operation station positioned around the rotating table must have a stopping time sufficient to allow said operation station to carry out the corresponding control.
The technical problem at the base of the present disclosure is to increase the efficiency of a control apparatus of the above-mentioned type, increasing the number of pieces which can be controlled per time unit and, at the same time, guaranteeing high precision in the control of dimensional tolerances ensuring, therefore, a stopping time for each control operation station sufficient to carry out the corresponding control. More in particular, the technical problem is to increase the efficiency of a control apparatus for all possible configurations of the control operation stations mounted around the rotating table, determining the speed with which the mechanical pieces are positioned on the rotating table according to the number of control operation stations mounted around it and according to the time necessary to carry out the control at each station.